The following describes a concrete construction of a currently-used positron emission tomography (PET) apparatus that images radiopharmaceutical distribution. The currently-used PET apparatus includes a detector ring having radiation detectors for detecting radiation arranged in a ring shape. The detector ring detects a pair of radiation (an annihilation radiation-pair) having opposite directions to each other and emitted from radiopharmaceutical within a subject.
Next, a construction of a radiation detector 51 is to be described. As illustrated in FIG. 23, the radiation detector 51 includes a scintillator 52 having scintillation counter crystals arranged three-dimensionally, and a light detector 53 configured to detect fluorescence from γ-rays absorbed into the scintillator 52. The radiation detector 53 has detection surfaces of light detecting elements 53a arranged in a two-dimensional matrix. The detection surface of the light detector 53 is optically connected to one surface of the scintillator 52. See U.S. Pat. No. 7,071,474.
Radiation entering into the scintillator 52 is converted into many photons to travel toward the light detector 53. Here, the photons travels through the scintillator 52 while spatially spreading to the detection surfaces of the light detector 53 arranged in a matrix. That is, many photons from fluorescence are split into many detecting elements 53a to be detected simultaneously.
The radiation detector 51 determines a position in the scintillator 52 where fluorescence is emitted using detection data of the fluorescence that is captured by a plurality of detecting elements 53a. That is, the radiation detector 51 determines a position of the center of gravity in a luminous flux of fluorescence on the detection surface by the detecting element 53a. The position of the center of gravity means a position where fluorescence has been generated. Data on the position is used when radiopharmaceutical within the subject is mapped.